1. Field of the Invention
The present invention relates to optical devices and, more particularly, to a multibeam deflector having a plurality of optical deflection devices.
2. Description of the Related Art
Optical deflectors are classified into a mechanically-operated optical deflector, such as a vibration galvanometer or a polygon mirror, and a non-mechanically-operated optical deflector, such as an acousto-optic device and an electro-optic device. The mechanically-operated optical deflector has been used practically in many laser printers and barcode readers. However, the mechanically-operated optical deflector includes a mechanically-operated part, which may cause a problem in achieving a high-speed operation and high integration. Thus, the application range of the mechanically-operated optical deflector is limited.
On the other hand, the non-mechanically-operated optical deflector does not include a mechanically-operated part, and is controlled optically or using electric signals. The non-mechanically-operated optical deflector is suitable in achieving a high-speed operation and also has an advantage that an optical system incorporated therein can be made compact. Thus, practical use of the non-mechanically-operated optical deflector is expected.
However, there is a problem in that the non-mechanically-operated optical deflector is capable of performing optical deflection in only a single direction. For example, Japanese Laid-Open Patent Applications No. 59-192232 and No. 62-47627 disclose an optical device or optical deflector, which can perform an optical deflection within a plane parallel to a waveguide. This optical device or optical deflector deflects a light, which is transmitted in a waveguide, according to an acousto-optic effect or an electro-optic effect, and causes the deflected light to exit through a prism or a grating. However, the optical device or optical deflector deflects the light only in a single direction. In order to acquire optical deflection in a plurality of directions by using a generally-used non-mechanically-operated optical deflector, a structure which combines an optical deflector and an optical system is needed. However, a system size of a non-mechanically-operated optical deflector having such a structure may be increased inevitably.
Japanese Laid-Open Patent Application No. 58-125023 discloses a technique to cause a non-mechanically-operated optical deflector to deflect a light in a plurality of directions. According to this technique, a light transmitting in a waveguide can be deflected within an optical waveguide plane according to an acousto-optic effect, and the light transmitting in the waveguide can also be deflected in a direction perpendicular to the waveguide plane by changing a refraction index of the waveguide near an end surface of the waveguide according to a thermo-optic effect. Further, Japanese Laid-Open Patent Application No. 58-130327 also disclose a technique to deflect a light within an optical waveguide plane and also deflect the light in a direction perpendicular to the optical waveguide plane by changing a refraction index of a portion, in which an exit grating is formed, according to an electro-optic effect. These techniques can be used in principle to deflect a light into a plurality of directions.
However, the above-mentioned conventional techniques use an acousto-optic effect in deflecting a light within a plane parallel to an optical waveguide, and also use a thermo-optic effect or an electro-optic effect in deflecting a light in a direction perpendicular to an optical waveguide plane. The deflection according to an acousto-optic effect has a problem in that a deflection angle is extremely small and a response speed is low. The deflection according to a thermo-optic effect or an electro-optic effect has a problem in that a deflection angle is extremely small.
As mentioned above, a conventional non-mechanically-operated optical deflector is capable of deflecting a light only in a single direction. Additionally, even if the conventional non-mechanically-operated optical deflector is capable of deflecting a light in a plurality of directions, the deflection angle is not sufficient in practical use.